We present first results from a program to measure the chemical abundances of a large (N > 30) sample of thick disk stars with the principal goal of investigating the formation history of the Galactic thick disk. We have obtained high-resolution, high signal-to-noise spectra of 10 thick disk stars with the HIRES spectrograph on the 10 m Reck I telescope. Our analysis confirms previous studies of O and Mg in the thick disk stars, which reported enhancements in excess of the thin disk population. Furthermore, the observations of Si, Ca, Ti, Mn, Co, V, Zn, Al, and Eu all argue that the thick disk population has a distinct chemical history from the thin disk. With the exception of V and Co, the thick disk abundance patterns match or tend toward the values observed for halo stars with [Fe/H] approximate to -1. This suggests that the thick disk stars had a chemical enrichment history similar to the metal-rich halo stars. With the possible exception of Si, the thick disk abundance patterns are in excellent agreement with the chemical abundances observed in the metal-poor bulge stars, suggesting the two populations formed from the same gas reservoir at a common epoch. T

Thirteen red clump stars from Baade's window were observed with high resolution in the red part of the optical spectrum with the UVES echelle spectrograph at the Mount Paranal ESO Observatory. The model atmosphere abundance analysis placed their [Fe/H] values in a range from 0.0 to - 1.52 dex. Present results, based on direct measurements of iron abundance, confirm former suggestions that the I-band brightness of the red clump giants only weakly depends on [Fe/H].

By adding a prism-cross-dispersed echellette grating as an optional module to the Inamori Magellan Areal Camera and Spectrograph (IMACS), complete spectra from 3400 to 11000Angstrom of 15 simultaneous objects may be achieved with a resolution of R = 21,000 for a projected 0.5-arcsec slit width and a 5.0-arcsec slit length. The additional cost of this module is on the order of $50,000.

The trend of [Mn/Fe] in the Galactic bulge follows the solar neighborhood relation, but most stars in the Sagittarius dwarf spheroidal galaxy show [Mn/Fe] deficient by similar to0.2 dex. This leads us to conclude that the Mn yields from both Type Ia and Type II supernovae (SNe) are metallicity dependent. Our observations militate against the idea, suggested by Gratton, that Mn is overproduced by Type Ia SNe, relative to Type II SNe. We predict Mn/Fe ratios, lower than the solar neighborhood relation, for the younger populations of nearly all dwarf galaxies, and that Mn/Fe ratios may be useful for tracing the accretion of low-mass satellites into the Milky Way.

We discuss the detailed composition of 28 extremely metal-poor (EMP) dwarfs, 22 of which are from the Hamburg/ESO Survey (HES), based on Keck echelle spectra. Our sample has a median [Fe/H] of - 2.7 dex, extends to - 3.5 dex, and is somewhat less metal-poor than was expected from [Fe/H](HK, HES) determined from low-resolution spectra. Our analysis supports the existence of a sharp decline in the distribution of halo stars with metallicity below [Fe/H] = -3.0 dex. So far no additional turnoff stars with [Fe/H] < -3.5 have been identified in our follow-up efforts. For the best-observed elements between Mg and Ni, we find that the abundance ratios appear to have reached a plateau, i.e., [X/Fe] is approximately constant as a function of [Fe/H], except for Cr, Mn, and Co, which show trends of abundance ratios varying with [Fe/H]. These abundance ratios at low metallicity correspond approximately to the yield expected from Type II supernovae (SNe) with a narrow range in mass and explosion parameters; high-mass Type II SN progenitors are required. The dispersion of [X/Fe] about this plateau level is surprisingly small and is still dominated by measurement errors rather than intrinsic scatter. These results place strong constraints on the characteristics of the contributing SNe. The dispersion in neutron-capture elements and the abundance trends for Cr, Mn, and Co are consistent with previous studies of evolved EMP stars. We find halo-like enhancements for the alpha-elements Mg, Ca, and Ti, but solar Si/Fe ratios for these dwarfs. This contrasts with studies of EMP giant stars, which show Si enhancements similar to other alpha-elements. Sc/Fe is another case where the results from EMP dwarfs and from EMP giants disagree; our Sc/Fe ratios are enhanced compared to the solar value by similar to 0.2 dex. Although this conflicts with the solar Sc/Fe values seen in EMP giants, we note that alpha-like Sc/Fe ratios have been claimed for dwarfs at higher metallicity. Two dwarfs in the sample are carbon stars, while two others have significant C enhancements, all with C-12/C-13 similar to 7 and with C/N between 10 and 150. Three of these C-rich stars have large enhancements of the heavy neutron capture elements, including lead, which implies a strong s-process contribution, presumably from binary mass transfer; the fourth shows no excess of Sr or Ba.

We outline the results of a study of the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). For the Sgr dSph stars with [Fe/H >= - 1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the alpha-elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old metal-poor population, including products of AGB stars and type la supernovae (SN).

We present copper abundances for 14 red giant stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph), showing that [Cu/Fe] is deficient by similar to 0.5 dex, relative to the Galactic trend. This is most easily understood as due to an enhanced contribution of iron peak nucleosynthesis products from Type Ia supernovae (SNe Ia). The deficient [Cu/Fe] ratios might also be the result of a metallicity-dependent yield from SNe Ia, similar to previous conclusions for Mn, although SN Ia nucleosynthesis predictions suggest a negligible Cu yield. The enhanced SN Ia products, suggested by our low [Cu/Fe] ratios, fit a leaky box chemical evolution scenario for the Sgr dSph, where ejecta from the old, metal-poor, population overwhelmed nucleosynthesis products from younger generations, resulting in young stars with uncharacteristic compositions. The only other system known to have unusually low [Cu/Fe] is the Galactic globular cluster omega Cen, which, like the Sagittarius dwarf galaxy, has strong enhancements of s-process elements. Thus, our copper abundances lend support to the idea that omega Cen is the remaining nucleus of an accreted dwarf galaxy.

We present abundance results from our Keck/HIRES observations of giants in the Galactic Bulge. We confirm that the metallicity distribution of giants in the low-reddening bulge field Baade's Window can be well-fit by a closed-box enrichment model. We also confirm previous observations that find enhanced [Mg/Fe], [Si/Fe] and [Ca/Fe] for all bulge giants, including those at super-solar metallicities. However, we find that the [O/Fe] ratios of metal-rich bulge dwarfs decrease with increasing metallicity, contrary to what is expected if the enhancements of the other a-elements is due to Type II supernovae enrichment. We suggest that the decrease in oxygen production may be due to mass loss in the pre-supernova evolution of metal-rich progenitors.

We present lithium abundances for 28 halo subgiants based on high resolution, high signal-to-noise ratio spectra. Excluding the known lithium-rich subgiant BD +23 3912, the maximum abundances are log epsilon(Li) = 2.35. While subgiants evolve from stars hotter than the main sequence turn-off with shallower convection zones that may have depleted lithium to a lesser degree, lithium abundances in halo subgiants are not in agreement with the primordial value as predicted from standard big bang nucleosynthesis combined with recent results from WMAP.